1. Field of the Invention
The present invention relates to a method for discriminating recording medium that discriminates the kind thereof, and a recording apparatus, which is provided with a function to discriminate the kind of recording medium. The invention also relates to a program that executes the discrimination of the kind of recording medium, and a storage that stores such program as well. More particularly, the invention relates to the technology of discriminating the kind of recording medium in accordance with image information obtainable form the surface of recording medium.
2. Related Background Art
Conventionally, as the output apparatus of a printing system that expels recording medium having images recorded thereon by the formation of color images with the adhesion of color toners or ink on the recording surface of such recording medium, there have been made available those of various methods, such as electro-photographic method, wire-dot method, and ink jet method, among some others.
Of the aforesaid methods, the ink jet method provides a mode, in which ink is directly discharged form a recording head to a recording medium, with such advantages that the number of processes required up to the formation of images on a recording medium is smaller; the running cost is economical; and the method is preferably suitable for color recording with a lesser amount of noises at the time of recording operation. With these advantages, this method is given particular attention in the wide range of application fields for office to home use. In recent years, the output apparatus having the ink jet method applied thereto has been widely adopted for a recording apparatus (a printer), facsimile equipment, a copying machine, and many others.
It is generally known that the recording apparatus that adopts the ink jet method is capable of using various kinds of recording medium adequately depending on the uses. As the kind of recording medium, there are a plain paper sheet, which is generally used irrespectively of recording methods; a coated paper sheet for ink jet use (including postcard size greeting cards or the like dedicated to ink jet use) treated with coating agent, such as silica, on the recording surface of the recording medium in order to suppress ink spread and obtain a better coloring effect; a glossy paper sheet and a glassy film, which are used for the formation of photograph or image like a photographic glossy print sheet having glossiness on the recording surface of the recording medium; an OHP film for use of transparent source document; a transfer paper sheet for transferring images to a T-shirt or other cloth by use of an iron after recording them on the recording medium; and a back printing film, which has the recording face on the backside of the recording medium, among some others. There are many kinds of various mediums, beginning with those regularly and often used by the users.
For the recording apparatus of the ink jet method, the recording conditions under which a good recording image is made obtainable are different by the kind of recording medium, because the permeability and fixation of ink are different depending on the coating agent applied to the surface of a recording medium. Consequently, before the initiation of recording on a recording medium, the user must select or set by input the kind of the recording medium to be used for recording so as to set a suitable recording mode for the kind of recording medium. Then, however, if the user should wrongly set the suitable recording mode for the kind of the recording medium to be used, the user may fail in obtaining the quality of recorded image as desired in some cases. In order to avoid the user's complicated operation and wrong setting, there have made studies for the development of an apparatus capable of automatically discriminating the kind of recording medium in order to select and set the optimal recording mode. The setting of a recording mode, which is preferably suitable for the kind of a recording medium to be used, is not only needed for the recording apparatus of the ink jet method, but also, needed for those of other methods.
Here, as one of the methods for discriminating the kind of recording medium, there is cited a method for measuring the light intensity with the reflection light from the surface of a recording medium by use of the optical sensor that adopts the photoelectric converting element with the irradiation of light from the light source structured as shown in FIG. 31. In FIG. 31, a reference numeral 3101 designates a light source that irradiates light on a recording medium 3103, the target recording medium, the kind of which should be discriminated, at an incident angle θ (any value). Also, a reference numeral 3102 designates a light-receiving element that receives the regularly reflected light, that is, the light reflected from the light irradiated from the light source 3101 at a reflecting angle θ equal to the incident angle θ, which measures the intensity of the regularly reflected light. The intensity of this regularly reflected light changes depending on the degree of glossiness of the surface, thus making it possible to know that of the target-recording medium. The arrangement position of the light source 3101 and light-receiving element 3102 is established so that the light-receiving element 3102 is able to receive the regularly reflected light reflected from the surface of the recording medium 3103 when irradiated by the light from the light source 3101. For the light-receiving element 3102, a photodiode, a phototransistor, or some other semiconductor device is used. In accordance with the conventional structure, it has been practiced to made discrimination of the kind of recording medium by means of comparison between the intensity of the regularly reflected light thus obtained, and the intensity of the regular refection light of the kind of the recording medium, which has been measured in anticipation of the use thereof.
Also, there is a disclosure in the specification of Japanese Patent Application Laid-Open No. 11-271037 as to the image formation method and image formation apparatus whereby to form a high-quality image without depending on the kind and the surface roughness of a recording medium to be used. In the specification of this application, it is disclosed that the intensity distribution of the reflection light from a recording medium is detected as the three-dimensional image information when light is irradiated to the recording medium from the light source, and subsequently, the surface roughness is detected by converting such information into the fractal that serves as the one-dimensional information, thus controlling the toner amount appropriately to match the surface roughness of the recording medium.
However, in the conventional technology that has been described above, problems are encountered as given below.
There is a tendency that the intensity of the regularly reflected light, that is, glossiness, presents the value proportional to the surface roughness for recording medium formed by the same material. Therefore, this can be used as parameters for discriminating the kind of recording medium. However, most of the various kinds of recording medium use different materials, and there are some of them that actually indicate almost the same intensity of regularly reflected light even if the kind of recording medium are different. One of the examples therefor is the coated sheet for ink jet use. FIG. 32 shows such relations.
FIG. 32 is a view that shows the relations between each recording medium and the intensity of regularly reflected light. A reference numeral 3201 designates the intensity of regularly reflected light obtainable from a plain sheet. Likewise, a reference numeral 3202 designates that of a coated sheet for ink jet use; 3203, that of a glossy sheet; 3204, that of a glossy film; and 3205, that of an OHP film, respectively. As shown in FIG. 32, the intensities of the regularly reflected light obtainable form the plain sheet and the coated sheet for ink jet use are overlapped with each other within a range of 3206.
The coated sheet for ink jet use has higher smoothness than that of the plain sheet (the value of which becomes larger for the flatter and smoother surface of the recording medium). Therefore, the intensity of regularly reflected light becomes larger for the coated sheet for ink jet use than the plain sheet if the recording medium use the same material. However, silica or other agent coated on the surface of the coated sheet for ink jet use allows light dispersion to be increased. Then, the resultant value of the regularly reflected light becomes the same as or slightly smaller than that of the plain sheet.
As described above, it is not easy to discriminate the plain sheet from the coated sheet for ink jet use only in accordance with the values of regularly reflected light. Therefore, this presents a large problem for the recording apparatus of ink jet method, because there is a need for different recording condition, such as the amount of ink discharge, the number of passes, which is the scanning frequency of the recording head for recording image of one-line portion, and some others, under which the recording apparatus of ink jet method should operate. Particularly, with respect to these two kinds of recording medium, recording conditions differ from each other greatly, which makes it necessary to discriminate one kind of recording medium from the other exactly.
Also, for the recording apparatus of electro-photographic method, other than the recording apparatus of ink jet method, there is a fear that if the user should set the coated sheet for ink jet use, which is wrongly taken as the plain sheet, in a cassette for retaining recording the recording medium, the coated sheet may be wound around the fixing roller. Like this, it becomes necessary not only for the recording apparatus of ink jet method, but also, for those of other methods to discriminate exactly the various kinds of recording medium, which are on the market widely.
In order to solve the aforesaid problem, there has been proposed a structure shown in FIG. 33, in which a reflective optical sensor is used to measure not only the component of regularly reflected light, but also, to measure the diffused reflection light component. In FIG. 33, a reference numeral 3301 designates a light source that irradiates light on a recording medium 3303, the target recording medium, the kind of which should be discriminated, at an incident angle θ (any value). Also, a reference numeral 3302 designates a light-receiving element that receives the regularly reflected light, that is, the light reflected from the light irradiated from the light source 3301 at a reflecting angle θ equal to the incident angle θ, which measures the intensity of the regularly reflected light, that is, to measure the glossiness. Further, a reference numeral 3303 designates a light receiving element that receives the diffused reflection light, which reflects at an angle different from the incident angle θ of the light irradiated from the light source 3301 (in FIG. 33, which is the light reflected at an angle perpendicular to the recording medium), and measures the intensity of the diffused reflection light. The intensity of this reflected light changes depending on the white degree of a recording medium. Therefore, this makes it possible to know the whiteness of the recording medium. The arrangement position of the light source 3301 and the light receiving element 3302 that receives the regularly reflected light, is set so that the regularly reflected light irradiated from the light source 3301, which reflects from the recording surface of a recording medium 3304, can be received by the light receiving element 3302. Likewise, the arrangement position of the light source 3301 and the light receiving element 3303 that receives the diffused reflection light, is set so that the diffused reflection light irradiated from the light source 3301, which reflects from the recording surface of the recording medium 3304, can be received by the light receiving element 3303. Here, the discrimination is made for the kind of recording medium by comparison between the intensities of the two reflection lights obtained by the structure thus arranged, and the intensity of reflected light of the kind of a recording medium anticipated to be used, which is measured in advance.
In this case, the discrimination between the plain sheet and the coated sheet for ink jet use is made mainly in accordance with the difference in the intensities of diffused reflection lights, that is, the difference in whiteness thereof. FIG. 34 shows such relations. FIG. 34 is a view that shows the relations between each recording medium and the regularly reflected light, and the diffused reflection light as well. A reference numeral 3401 designates the distribution area of the plain sheet with respect to the intensity of the regularly reflected and that of the diffused reflection light. Likewise, a reference numeral 3402 designates the distribution area of the coated sheet for ink jet use; 3403, that of the glossy sheet; 3404, that of the glossy film; and 3405, that of the OHP film, respectively. The whiteness of the coated sheet for ink jet use is higher than that of the plain sheet. Therefore, it is known that the overlapping area thereof is made smaller than that of the plain sheet and the coated sheet for ink jet use, which are measured by use of only the regularly reflected light shown in FIG. 32. Nevertheless, as shown in FIG. 34, the distribution areas of the plain sheet and coated sheet for ink jet use may be overlapped even by the application of the intensities of the diffused reflection lights for both of them, which makes it difficult to make the discrimination of the kind exactly.
Now, hereunder, the description will be made of the problems with respect to the structure that uses the reflective sensor, including the aforesaid reasons.
1. Conventionally, the coating of calcium carbonate to the surface of a recording medium has not been preferred due to the problem that the fixing roller of a copying machine is worn off by the coating thereof. However, along with the durability of the fixing roller, which has been made higher, this coating is now widely used. The coating of calcium carbonate is effective in enhancing the whiteness of a recording medium, while it becomes more difficult to discriminate the plain sheet having higher whiteness with the coating of calcium carbonate from the coated sheet for ink jet use.
2. In order to suppress the influences resulting from the variations of light sources, it is generally practiced to use a structure that adopts the comparison between the values of the intensities of regularly reflected light and diffused reflection light as the parameters for making the discrimination of the kind of recording medium. However, for the recording medium the kind of which are different, there exist some of them that indicate the same value when the comparison is taken, although the absolute values of the respective intensities of the regularly reflected light and diffused reflection light are different, which makes it difficult to make the discrimination of the kind of recording medium. Also, when the absolute values of the intensities of the regularly reflected light and diffused reflection light are used for parameters to discriminate the kind of the recording medium, not the comparative values between them, there is a need for highly precise correction, which should unavoidably lead to the increased costs of a recording apparatus. Further, it is necessary to consider such correction not only at the time of delivery of the apparatus, but also, consider it in terms of aging deterioration thereof. This makes it difficult to make the discrimination of the kind of recording medium always in good precision.
3. Even with such highly precise correction as described above, the measured values of the plain sheet and coated sheet for ink jet use tend to vary greatly depending on the location where the measurement is given. Therefore, measurements are needed for plural locations. In other words, the movement of the sensor used for measuring the reflected light or the movement of a target-recording medium becomes prerequisite for the measurement of an exact value, which necessitate the provision of a mechanical structure. Also, it takes a time for the sensor that measures the reflected light or it takes a time for effectuating measurements at plural locations along with the movement of a recording medium. As a result, the user is forced to endure a waiting time.